1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser printer, a copier, or the like that utilizes an electrophotography recording method.
2. Description of the Related Art
An image forming apparatus utilizing an electrophotographic method includes an optical scanning device configured to condense laser light emitted from a laser diode to form an image on a photosensitive member by a lens and expose the photosensitive member. The optical scanning device performs, in order to maintain desired image quality under various exposure conditions, adjustment so that the amount of laser light emitted from the laser diode becomes a desired value.
Specifically, in a case of exposing the photosensitive member using light emitted from the chip front side of the laser diode, laser light emitted from behind the chip is received at a photodiode disposed behind the chip. Next, so-called auto power control (APC) is performed for adjusting the amount of emitted laser light based on output from this photodiode. Japanese Patent Laid-Open No. 2003-305882 describes, regarding APC, a method for adjusting the amount of light emitted from a laser diode by feeding back a comparison value between a voltage value converted from monitor current generated based on the amount of received light detected at the photodiode and a reference voltage value set from a duty value of a pulse width modulation (PWM) signal. The reason why the amount of emitted laser light is adjusted using the light received behind the chip is based on a premise that the amount of light that is emitted from behind the chip and received by the photodiode is proportional to the amount of light emitted from the front of the chip to form an image on the photosensitive member. That is to say, detecting laser light emitted from behind the chip is substantially the same as detecting light emitted from the front of the chip to form an image on the photosensitive member.
High image quality has increasingly been demanded for image forming apparatuses using the electrophotography method in recent years. For example, the image forming apparatus disclosed in Japanese Patent Laid-Open No. 2012-137743 irradiates locations of the photosensitive member where toner is to be adhered with laser light at a normal emission level (first emission level) for normal printing. In addition, the image forming apparatus suppresses occurrences such as a normal fogging phenomenon and so forth by irradiating a location of the photosensitive member on which no toner is adhered, thereby forming an image with high image quality with laser light at a minute emission level (second emission level) lower than the emission level for normal printing.